Projecting loads or loads that tend to buckle cannot be hoisted with a single hook and belts. Such loads require the attachment of a lifting beam, from which the belts or other load suspension means are suspended in order to attach the load. This method is widely used, but has the disadvantage that the lifting beam must be replaced with another lifting beam when the dimensions of the load change.
Alternatively, it is also known to utilize chain hoists in the form of so-called dual chain hoists, in which two chain hoists are suspended from a lifting beam. These two chain hoists are usually actuated by a single drive motor for reasons of synchronization. The disadvantage of such chain hoists is the fixed spacing between the hooks that may be excessively small or excessively large. In order to adapt these hoists to the size of the load, it is once again required to use lifting beams at the height of the hooks or traction cables in order to increase or decrease the spacing between the hooks in accordance with the dimensions of the load.
Another disadvantage of such dual chain hoists results from the residual length, i.e., the smallest distance that the hooks can be from a building or wall when the dual chain hoist is moved in the direction of the wall. The remaining length increases considerably if the hooks are pulled toward one another with corresponding means.